Simmons announced her departure Thursday in a letter sent to students, faculty and alumni. She said that after 11 years the time was right to move on and prepare the university for new leadership.

“I want more than anything for Brown to be successful,” the 66-year-old Simmons told The Associated Press. “I think it’s part of my responsibility as a president who cares deeply about Brown to also care about what happens when I leave.”

Simmons plans to leave her position at the end of the academic year. She said she will work on two books — one an autobiography and another on education — before returning to Brown to work as a professor of comparative literature and Africana studies.

Simmons became Brown’s president in 2001 after serving as president of Smith College in Northampton, Mass.

Under her leadership, Brown increased its faculty by 20 percent, expanded beyond its historic campus, established the Brown Institute for Brain Science and undertook a $1.4 billion fundraising campaign.

Simmons also created a panel to investigate Brown’s historic ties to slavery and worked to expand academic ties to schools in Asia and ones closer to home, including the Rhode Island School of Design.

Brown Chancellor Thomas J. Tisch said of Simmons: “She has paid careful attention to every critical facet of the university, from renewing our commitment to shared governance, to reaffirming our essential role in tackling even the thorniest issues through respectful and informed civil discourse.”

Luiz Fernando Valente, the chairman of faculty when Simmons was appointed president, called her the most effective leader he has seen at Brown since he joined the faculty in 1983.

“Eleven years is a lengthy tenure, but I was hoping for 12,” said Valente, a professor of Brazilian and Portuguese studies and literature. “She immediately struck me as very honest, straightforward and no-nonsense. She was the right person for Brown.”

“Even among its many bright lights, she shone brightest,” said Chafee, who accepted a visiting fellowship at Brown’s Watson Institute for International Studies in 2006.

Simmons, asked if she had any regrets from her time as president, answered without pause.

“I have not done a fifth of what I hoped I could do,” she said. “Universities are complex places, and the amount of time it takes to do things is much longer than almost anyone anticipates.”

One controversy during Simmons’ tenure centered around Brown’s response to a 2006 rape allegation by one student against another. Former student William McCormick III later sued in federal court, saying he was falsely accused of rape and then unfairly pressured to leave the university.

McCormick accused the university of failing to properly investigate the rape complaint and said that administrators were influenced in their handling of the case by their relationship to the accuser’s father, who is a major Brown donor.

The university has said it acted appropriately. Simmons said the lawsuit played no role with her decision to resign.

McCormick’s lawyer, J. Scott Kilpatrick, said Simmons’ departure may “mean nothing” to the case, “but one can hope that it might mean a somewhat more open-minded or even self-reflective view of how Brown handled this matter.”

Simmons’ position on the board of Goldman Sachs also generated controversy last year after board members approved bonuses for executives, including a $9 million payout to bank chairman and chief executive Lloyd C. Blankfein.

Her decade-long role at Goldman went largely unnoticed on campus until student Simon Liebling wrote an opinion column last year in the university newspaper, The Brown Daily Herald.

“She tied Brown to the single most egregious example of corporate excess to emerge from the recession,” Liebling, 21, said in an interview.

Simmons did not stand for re-election to Goldman’s board at the annual shareholders’ meeting last year after collecting more than $320,000 in compensation for her work the year before. She said at the time she was stepping down to devote more time to Brown.

Liebling, a senior history major from Highland Park, N.J., also criticized Simmons for running Brown like a corporation rather than a nonprofit educational institution by emphasizing building projects and fields of study such as engineering and medicine.

“Her administration has not taken pride in what made Brown Brown and has instead sought to turn it into another Harvard, another Yale or another Princeton,” Liebling said.

Simmons’ departure stunned students who say Facebook lit up with pleas for her to stay as soon as she announced her departure. She was popular among students, who have sold T-shirts displaying her image to raise money for campus activities.

Patrice Groomes, a 17-year-old freshman from Chicago, said Simmons was one of the reasons she chose Brown.

“As a black woman, I feel empowered by the fact that she’s black and female,” said Groomes, who first met Simmons while visiting the campus with her father when she was in middle school.

Christina Lam, a 21-year-old junior from Columbus, Ohio, said she was puzzled by the decision.